Process for manufacturing a superconducting composite

ABSTRACT

A superconducting composite comprising a compound oxide type superconductor and an outer metal pipe on which said superconductor is supported, characterized in that (i) said outer metal pipe is made of at least one of metals selected from a group comprising gold, silver and platinum metals and their alloys or (ii) an intermidiate layer made of these precious metals is interposed between the compound oxide and the metal pipe. 
     The composite may be in a form of a solid pipe or a hollow pipe having a superconducting thin layer deposited on an inner surface of the metal pipe.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a composite having superconductingproperty and a process for manufacturing the same. Particularly, itrelates to a process for manufacturing a superconducting composite, suchas a wire having higher and stable critical temperature and criticalcurrent density.

2. Description of the Related Art

Under the superconducting condition, the perfect diamagnetism isobserved and no difference in potential is observed for all that anelectric current of a constant finite value is observed internally, andhence, a variety of applications of superconductivity have been proposedin a field of electric power transmission as a mean for deliveringelectric power without loss.

The superconductivity can be utilized in the field of power electricapplications such as MHD power generation, power transmission, electricpower reservation or the like; in the field of transportation such asmagnetic levitation trains or magnetically propelling ships; a highsensitive sensors or detectors for sensing very weak magnetic field,microwave, radiant ray or the like, in the medical field such ashigh-energy beam radiation unit, in the field of science such as NMR orhigh-energy physics; or in the field of fusion power generation.

In addition to the abovementioned power electric applications, thesuperconducting materials can be used in the field of electronics, forexample, as a Josephson device which is an indispensable switchingdevice for realizing a high-speed computer which consumes very reducedpower.

However, their actual usage have been restricted because the phenomenonof superconductivity can be observed only at very low cryogenictemperatures. Among known superconducting materials, a group ofmaterials having so-called A-15 structure show rather higher Tc(critical temperature of superconductivity) than others, but even thetop record of Tc in the case of Nb₃ Ge which showed the highest Tc couldnot exceed 23.2 K. at most. This means that liquidized helium (boilingpoint of 4.2 K.) is only one cryogen which can realize such very lowtemperature of Tc. However, helium is not only a limited costly resourcebut also require a large-scaled system for liquefaction. Therefore,there had been a strong demand for another superconducting materialshaving higher Tc. But no material which exceeded the abovementioned Tchad been found for all studies for the past ten years.

It has been known that certain ceramics material of compound oxidesexhibit the property of superconductivity. For example, U.S. Pat. No.3,932,315 discloses Ba-Pb-Bi type compound oxide which showssuperconductivity and Japanese patent laid-open No. 60-173,885 disclosesthat Ba-Bi type compound oxides also show superconductivity. These typesuperconductors, however, possess a rather lower transition temperatureof about 10 K. and hence usage of liquidized helium (boiling point of4.2 K.) as cryogen is indispensable to realize superconductivity.

Possibility of existence of a new type of superconducting materialshaving much higher Tc was revealed by Bednorz and Muller who discovereda new oxide type superconductor in 1986 [Z. Phys. B64 (1986)189]

This new oxide type superconducting material is [La, Ba]₂ CuO₄ or [La,Sr]₂ CuO₄ which are called as the K₂ NiF₄ -type oxide having a crystalstructure which is similar to known perovskite type oxide. The K₂ NiF₄-type oxides show such higher Tc as 30 K. which are extremely higherthan the known superconducting materials and hence it becomes possibleto use liquidized hydrogen (b.p.=20.4 K.) or liquidized neon (b.p.=27.3K.) as a cryogen which bring them to exhibit the superconductivity.

It was also reported in the news parer that C. W. Chu et al discoveredin the United States of America another type of superconducting materialhaving the critical temperature of in the order of 90 K. in February1987, and hence possibility of existence of high-temperaturesuperconductors have burst on the scene.

However, the above mentioned new type superconducting materials whichwas just born have been studied and developed only in a form of sinteredbodies as a bulk produced from powders but have not been tried to beshaped into a wire form. The reason is that the new type superconductorsare ceramic materials of compound oxide which do not possess enoughplasticity or can not be worked easily in comparison with well-knownmetal type superconducting materials such as Ni-Ti alloy, and thereforethey can not or are difficult to be shaped or deformed into an elongatedarticle such as a wire by conventional technique such as wire-drawingtechnique in which superconducting metal is drawn directly or inembedded condition in copper into a wire form.

Still more, the above mentioned sintered ceramic materials must beshaped into an elongated structure when they are used as asuperconducting wire in practice. However, the above mentionedsuperconducting materials obtained in a from of a sintered body are veryfragile and are apt to be broken or cracked under even very weakmechanical stress. And hence, when they are shaped into a wire, specialattention must be paid for their handling in order not to be broken.

It is proposed in Japanese patent laid-open No. 61-131,307 a method formanufacturing a superconducting wire from a metal type superconductingmaterial which is apt to be oxidized and very fragile such as PbMo₀.35S₈, comprising charging the material metal powder in a metal shell,extruding the metal shell filled with the material powder at atemperature of higher than 1,000° C., and then drawing the extrudedcomposite. This metal working technique, however, can not apply directlyto ceramic material consisting of compound oxide, because the compoundoxide type superconducting materials can not exhibit thesuperconductivity if not the specified or predetermined crystalstructure is realized. In other words, a superconducting wire whichshows higher critical temperature and higher critical current densityand which is useable in actual applications can not be obtained outsidepredetermined optimum conditions. In particular, if the shell is notselected from proper materials, the resulting compound oxide will bereduced due to chemical reaction with the metal of the shell, resultingin poor or inferior properties of superconductivity.

A polycrystal having completely uniform crystal structure can not beobtained from particles having superconducting properties alone. Stillmore, the phenomenon of superconductivity is apt to be easily broken instronger magnetic field and under the fluctuation or unhomogeneousdistribution of temperature in the sintered body as well as theabovementioned oxide type superconducting materials possess ratherhigher specific resistance and lower heat-conductivity above thecritical temperature. Therefore, if the phenomenon of superconductivitybreaks locally, the sintered body produces Joule heat caused by thesuperconducting current preserved therein and explosive evaporation ofcryogen is induced when the heated portion of the sintered body contactswith the cryogen. In order to avert this danger, in conventional metaltype superconducting material, superconducting metal is shaped in a formof a fine wire or filament a plurality of which are embedded inelectroconductive metal which play a roll of a by-pass of electriccurrent when superconductivity break.

The oxide type superconducting materials are, however, difficult to beshaped or deformed into such filaments, because they have not enoughplasticity or processability in comparison with well-known metal typesuperconducting materials such as Ni-Ti alloy.

In order to realize a reliable and practical superconducting structure,it is indispensable that the structure possesses enough strength andtenacity which is sufficient to endure bending force during usage andalso has as finer cross sectional dimension as possible in such mannerthat it can transmit currency at higher critical current density and athigher critical temperature. However, conventional techniques can not orare difficult to produce wire shaped ceramic articles possessingsatisfactory mechanical strength and tenacity as well as a higherdimensional ratio of length to cross section.

Taking the abovementioned situation into consideration, the presentinventors have proposed processes for producing sintered ceramic wireshaving a practically usable higher dimensional ratio of length to crosssection without using organic binder which is a cause of deteriorationof strength and tenacity in U.S. patent application Ser. No. 152,713titled "Process for manufacturing a superconducting wire of compoundoxide-type ceramic" filed in Feb. 5, 1988 and Ser. No. 161,480 titled"Process for manufacturing a compound oxide-type superconducting wire"filed in Feb. 28, 1988 in which a metal pipe filled with material powderis subjected to plastic deformation such as wire-drawing technique bymeans of a die and then is sintered.

These solutions are themselves satisfactory but the present inventorshas continued to develope another process which can produce a ceramicwire possessing higher strength and no breakage and complete the presentinvention.

Therefore, an object of the present invention is to overcome theabovementioned problems of the conventional technique and to provide animproved process for producing a superconducting wire-like compositewhich has a higher Tc and higher stability as superconductor which canbe applicable to practical uses.

SUMMARY OF THE INVENTION

The present invention provides a wire-like composite comprising acompound oxide type superconductor and an outer metal pipe on which saidsuperconductor is supported, characterized in that a layer composed ofat least on of precious metals selected from a group comprising gold,silver and platinum metals and their alloys is interposed at aninterface between the compound oxide type superconductor and the outermetal pipe.

More precisely, according to the present invention, the wire-likecomposite including a compound oxide type superconductor and an outermetal pipe on which said superconductor is supported is characterized inthat

(i) said outer metal pipe is made of at least on of metals selected froma group comprising gold, silver and platinum metals and their alloys, or

(ii) an intermediate layer composed of at least on of metals selectedfrom a group comprising gold, silver and platinum metals and theiralloys is interposed between said compound oxide type superconductor andsaid outer metal pipe.

Now, each of the cases (i) and (ii) will be described in more indetails.

CASE I The Outer Metal Pipe is made of Precious Metals

(I-1) A solid composite

In this case, the outer metal pipe is made of Ag, Au or platinumelements of Pd. Pt. Rh. Ir. Ru. Os or their alloys and surrounds orcovers a sintered body of compound oxide.

According to this embodiment, the superconductor is compacted in theouter metal pipe made of precious metals having a lower electricalresistance, a higher specific heat and a higher heat conductivity, sothat the resulting solid wire-like composite shows higher mechanicalstrength because a fragile sintered article is supported by a metallicsheath having relatively higher strength and tenacity than the sinteredarticle.

Still more, according to the present invention, oxygen contents in thesuperconducting sintered body can be stabilized because of the presenceof the outer metal pipe. In fact, the oxygen contents of theabovementioned compound oxides such as an oxide containing a IIa elementand a IIIa element which can be used advantageously in the presentinvention may vary or change if they contact directly with a metal whichis liable to be oxidized. To solve this problem, according to thepresent invention, the outer metal pipe is made of at least one ofprecious metals selected from gold, silver, platinum metals or theiralloys to enclose the oxide therein so that the variation of oxygencontents in the compound oxide is suppressed.

An inner surface of the metal pipe may further have a protective layerwhich resists to oxidation so that the oxygen contents in the compoundoxide is maintained within an optimum range. This protective layer maybe made of an oxide such as AgO produced by oxidizing the inner surfaceof the metal pipe.

The outer metal pipe may have perforations or through holes which make apart of the superconductor open to an atmosphere. To realize suchstructure, the outer metal pipe may be made of a cylindrical wirenetting surrounding tightly the solid superconductor.

A metal wire or wires may be embedded in the superconductor. The wiresare preferably surface-treated with a material which is inert orinactive with respect to the superconductor.

The solid composite abovementioned is produced by a process according tothe present invention characterized by the steps comprising preparing atleast one of material powders selected from a group comprising

(i) a powder mixture of compounds each containing at least one ofconstituent elements of the compound oxide and

(ii) a sintered powder of compound oxide prepared by sintering thepowder mixture of (i) and then by pulverizing obtained sintered body,

compacting the material powder in a metal pipe made of at least on ofmetals selected from a group comprising gold, silver and platinum metalsand their alloys, and then heating the metal pipe filled with thematerial powder at a temperature ranging between an upper limitcorresponding to the lowest melting point of any one of constituentcomponents in the material powder and a lower limit which is lower by100° C. than said upper limit to sinter said material powder inside theouter metal pipe.

Each of the compounds may be an oxide powder or an carbonate powder ofconstituent elements of said compound oxide. An atomic ratio of elementsin said material powders may be adjusted to the same value as an atomicratio of constituent elements in said compound oxide to be produced.

The material powder may be compacted under a pressed condition and/ormay be granulated previously.

Wire-drawing may be performed during or after the sintering operation.It is also possible to heat-treat a sintered product at a temperatureranging from 160° C. to 700° C. The heat-treatment may be carried outafter wire-drawing but before the sintering operation.

Generally the sintering of the material powder may be carried out at atemperature ranging from 500° C. to 1,200° C. in which metal oxide suchas AgO is decomposed to Ag and oxygen which do not reduce the compoundoxide so that the oxygen contents in the oxide can be maintained at aconstant value which is beneficial to the crystal structure and/oroxygen deficiency of superior superconductor of compound oxides.

(I-2) A hollow composite of compound oxide

A hollow composite comprises an outer metal pipe made of Ag, Au orplatinum elements of Pd, Pt, Rh, Ir, Ru, Os or their alloys and a layerof compound oxide type superconductor applied or deposited on an innersurface of the metal pipe.

The layer of compound oxide type superconductor may be preferablydeposited by sputtering technique on an inner surface of the metal pipe.

The outer metal pipe may be closed at opposite ends thereof and/or maybe filled with inert gas. It is also possible to circulate a coolantthrough the interior of the hollow pipe.

It is also possible to reduce a cross section of the metal pipe bywire-drawing to obtain a finer pipe after the layer of compound oxidetype superconductor is formed on the inner surface of the metal pipe.

It is also possible to form an additional inner protective layerconsisting of a material which have lower coefficient of thermalexpansion on the superconducting compound oxide layer supported on theinner surface of the metal pipe. The material having lower coefficientof thermal expansion may be Si, zirconium, SiO₂ or glass.

The layer of superconductor may be formed also by wet-coating techniqueincluding application or coating of a thin film layer of superconductingmaterial containing a organic binder on the inner surface followed bysintering thereof.

CASE II An Intermediate Layer Made of Precious Metals is InterposedBetween the Outer Metal Pipe and the Superconductor

(II-1) A hollow composite

In this case, the outer metal pipe may be made of any metal such ascopper, iron or the like but an intermediate layer made of preciousmetals is interposed between the outer metal pipe and thesuperconductor.

The intermediate layer may be made of Ag, Au, Pd, Pt, Rh, Ir, Ru, Os ortheir alloys. The metals such as Pt, Au or the like which possessrelatively lower free energy (ΔG) for producing their oxides depositedon the inner surface of the metal pipe prevent chemical reaction betweenthe metal pipe with the compound oxide to preserve a constantcomposition of the superconductor. This intermediate layer may beproduced by any known technique such as vacuum-deposition, sputtering,plating, coating or cladding technique in which a precious metal pipe islined on the inner surface of the outer metal pipe.

The compound oxide type superconductor may be in a form of a layerdeposited on an inner surface of the intermediate layer deposited bysputtering technique or by wet-coating technique followed by sinteringoperation on an inner surface of said metal pipe.

An inner surface of said intermediate layer may be further coated withanother supporting layer made of one of materials which has strongadhesive property to said compound oxide type superconductor, or whichis stable to said compound oxide type superconductor, or which has arelatively lower thermal expansion coefficient with respect to thecompound oxide type superconductor such as Si, zirconium, SiO₂ or glass.

(II-2) A solid composite

In this case, the compound oxide type superconductor is in a form of asintered solid mass compacted inside the intermediate layer deposited onthe inner surface of the outer metal pipe according to theabovementioned method (II-1). The solid mass compacted in the metal pipemay be produced by the same procedure as (I-1).

Now, the present invention will be described with reference to attacheddrawings which illustrate preferred embodiments of the present inventionbut are not limitative of the present invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an illustrative cross sectional view of a solid compositeaccording to the present invention.

FIG. 2 is an illustrative cross sectional view which is similar to FIG.1 and which shows another embodiment of a solid composite according tothe present invention.

FIGS. 3A and 3B illustrate two variations of the solid composite shownin FIG. 2.

FIGS. 4A and 4B illustrate another embodiment of a composite accordingto the present invention, wherein FIG. 4A is a cross section thereof andFIG. 4B shows a side elevation thereof.

FIGS. 5A and 5B illustrate a variation of the composition shown in FIG.4, wherein FIG. 5A is a cross section thereof and FIG. 5B shows a sideelevation thereof.

FIGS. 6A and 6B illustrate still another embodiment of the presentinvention, wherein, FIG. 6A is a cross section thereof and FIG. 6B is aperspective view thereof.

FIGS. 7, 8 and 9 are cross sectional views of still another embodimentsof composites according to the present invention.

FIG. 10 is a cross section of a hollow composite according to thepresent invention.

FIG. 11 is an illustrative view of an apparatus which can be used formanufacturing continuously a composite having a tape-like configurationaccoding to the present invention.

Referring to FIG. 1 which illustrates a typical composite according tothe present invention, the composite shown in FIG. 1 is asuperconducting solid round wire comprising a core of a sinteredcompound oxide 11 and an outer metal pipe 12 made of precious metalsusch as silver or platinum surrounding tightly the sintered compoundoxide 11. In the following description, platinum is used as a meaterialof the metal pipe but is only an example of the material of the outerpipe. As shown, the pipe 12 surrounds and directly contacts the oxide11.

FIG. 2 illustrates another embodiment of a composite which is similar toFIG. 1 but a layer of PtO 23 is interposed between an outer Pt pipe 22and a sintered mass of compound oxide 21 compacted in the Pt pipe 22.The PtO layer 23 can be produced previously by heating an inner surfaceof the Pt pipe 22 in air and will supply oxygen produced by thermaldecomposition thereof at the following sintering stage to thesuperconducting material filled therein to control the oxygen contentsof the sintered compound oxide to a proper value.

Two variations shown in FIGS. 3A and 3B illustrate a rectangularsuperconducting wire or rod and a flat tape-like superconductoraccording to the present invention. In these variations, a sintered mass31a and 31b is enclosed in an outer Pt pipe 32a or in a platinum band32b through an interface layer of PtO 33a and 33b. The composite of FIG.3A may be produced by deforming a round pipe or by using a rectangularpipe or can be manufactured by a process including steps of moldingrectangular superconductor and then covering the molded article with ametal sheath.

Still another embodiment of a composite according to the presentinvention shown in FIGS. 4A and 4B is similar to the composite of FIG.1, but the outer pipe 42 has perforations or through-holes 44 which makethe inner core 41 exposed to surroundings. FIGS. 5A and 5B illustrate avariation of a composite shown in FIG. 4. The composite of FIG. 5 has arectangular cross section. In still another embodiment shown in FIG. 6,the outer metal pipe shown in FIG. 1 is displaced by a wire netting 62which envelopes an inner core of sintered compound oxide 61. In theembodiments of FIGS. 4 to 6, the core of compound oxides 41, 51 and 61can contact directly with atmosphere to permit to facilitate the controlof oxygen contents in the sintered compound oxide during sinteringstage.

FIGS. 7, 8 and 9 show three variations of solid composite according tothe present invention. In these embodiments, a plurality of platinumwires 84, 94 and 104 are embedded in a core of compound oxide typesuperconductor 81, 91 and 101 which is surrounded by an outer platinumpipe 82, 92 or an outer platinum band 102. In the embodiments shown, anoxide layer of PtO 83, 93 and 103 is interposed at an interface betweenthe core 81, 91 and 101 and the outer sheath 82, 92 and 102. The oxidelayer 83, 93 and 103 can be produced easily by heating in air an innersurface of the outer sheath 82, 92 and 102 to oxidize the same. Theexistence of the oxide layer 83, 93 and 103 is preferable to prevent theoxygen contents in the sintered compound oxide from being influenced bychemical reaction with a material of the pipe.

The composite shown in FIG. 8 is similar to that of FIG. 7, but containsa larger number and/or thicker platinum wires 94 in the superconductingcompound oxide core 91. In fact, if superconductivity is brokenaccidentally, a very high intensity of electric current must be passedby through the ordinary conductors composed of the outer metal pipe 92and embedded wires 94. Therefore, the embodiment shown in FIG. 8 ispreferable for applications requiring higher current intensity such aselectromagnets used in a strong magnetic field.

FIG. 10 illustrate a hollow composite according to the presentinvention. In this embodiment, an outer metal pipe 112 may be made ofprecious metals and any other metals such as copper. However, in thecase that the outer pipe 112 is not made of precious metal, an innersurface of the pipe 112 must have an inner lining layer or intermediatelayer of precious metal 113. This inner lining layer can be produced byconventional technique such as vacuum-deposition, sputtering,electroplating etc.

A hollow composite such as shown in FIG. 10 can be produced by thefollowing steps:

At first, powders of Y₂ O₃, Ba₂ CO₃ and CuO were mixed with such an atomratio of Y:Ba:Cu becomes to 1:2:3 and then the resulting mixture wascompacted and preliminarily sintered at 820° C. Then, the sintered massis pulverized and compacted again. This compact is further sintered at1,080° C. to produce a sintered block which is used as a target forsputtering.

Following is sputtering conditions to produce a thin film layer ofsuperconducting compound oxide on an inner surface of a platinum layerdeposited on an inner surface of a copper pipe having an inner diameterof 50 mm, a wall thickness of 2 mm and a length of 100 mm:

Oxygen partial pressure: 4×10⁻² Torr

Argon partial pressure : 3×10⁻² Torr

Substrate temperature : 700° C.

Substrate bias voltage: -600 V

High-frequency powder: 25 W/cm²

Deposition rate: 0.5 Å/sec

Total thickness: about 1 μm

FIG. 11 is a illustrative and diagrammatical drawing of an apparatuswhich can be applied to production of a composite according to thepresent invention continuously.

In this case, the material ceramic powder is preferably blended withorganic binder and can be prepared as following:

At first, powders of Y₂ O₃, Ba₂ CO₃ and CuO each having purity of morethan 3N and an average particle size of 5 μm were mixed with such anatom ratio that the proportions of Ba, Y and Cu in a composition of(Ba_(1-x) Y_(x))Cu_(y) O_(z) correspond to values of x=0.2 and y=1 andthen the resulting mixture was sintered in air at 920° C. for 12 hours.Then, the sintered mass is pulverized in mortar. After the sameprocedure of sintering and pulverization is repeated for three times,the resulting sintered powder is ground by high purity alumina balls ina ball mill for 5 hours to obtain a material powder having an averageparticle size of less than 5 μm.

The material powder is mixed and kneaded with a binder of PVB(polyvinylbutylal) in a solvent of toluene containing a plasticizer ofDBP (dibutylphtharate). The resulting paste is shaped into a sheethaving a thickness of 0.8 mm, a width of 300 mm and a length of 5 m anddried to ready to be used in an apparatus shown in FIG. 11.

The apparatus shown in FIG. 11 includes a continuous furnace beingprovided with two heating zones of a binder-removing zone 242 and asintering zone 243. An elongated shaped tape or wire 244 is supplied toan inlet of the binder-removing zone 242 from a coiler 245. Theelongated article 244 unwound from the coiler 245 is fed continuously tothe binder-removing zone 242 in which the elongated article 244 isheated at a temperature of 400° to 700° C. to remove the binder out ofthe elongated article 244.

After the binder-removing zone 242, the elongated article 244 is passedto a continuous lining station 246 which is positioned at the downstreamof the binder-removing zone 242. The continuous lining station 246 isprovided with a drum 248 for feeding a sheet 247 of precious metal oralloy to a guide 249 where the sheet 247 is wound around the elongatedarticle 247. A seam of the wound sheet 247 is welded by means of a laserwelder 220 so that the elongated article 244 is wrapped by the metalsheet 247.

The resulting composite comprising the elongated article 244 and thecovering sheet or outer sheath 247 is then passed to the sintering zone243 where the composite is heated at a temperature of 850° to 950° C. inoxygen containing atmosphere to sinter the elongated article. Thelongitudinal dimension or length of the sintering zone 243 and theadvancing velocity of the composite can be adjusted in such manner thatthe sintering is performed completely.

The product 241 thus obtained is cooled down slowly at a cooling speedof 8° C./min and may be wound about a drum 242 for stock. The productpossesses enough flexibility and self-supporting properties, since theelongated article 244 contains the binder. The apparatus shown in FIG.11 permits to carry out the sintering operation continuously at a higherproductivity.

The product produced by the abovementioned apparatus is furtherheat-treated for example at 700° C. for 36 hours under oxygen containingatmosphere to obtain a superconducting composite shown in FIG. 3B.

The composite shown in FIG. 9 can be also produced by the apparatusshown in FIG. 11. In this case, when the paste is shaped into a sheethaving a thickness of 0.8 mm, a width of 300 mm and a length of 5 m, forexample fifty platinum wires whose surface is oxidized previously arembedded in the sheet and dried to ready to be used in an apparatusshown in FIG. 11. In the apparatus, the binder is removed at 400° to700° C. and a silver sheath is put around the sheet. The resultingcomposite is heated in air at 935° C. for 5 hours to sinter the sheet.

The composite comprising the elongated compound oxide and the outermetal sheath produced by the present invention can be shaped or deformedinto a desired configuration such as a coil or the like due to thehigher flexibility and self-supporting property, so that the sinteringcan be performed in the condition of the coiled configuration or in acondition that the coiled is supported on any other conductive body. Theexistence of the sheath of Pt metal or its alloy also increase thedeflective strength.

The composites obtained by the abovementioned processes according to thepresent invention can be utilized in a variety of applications ofsuperconductors as they are. However, when a clearance which may occureventually between the outer metal pipe and the sintered compound oxidecore is undesirable, the composite can be further caulked or wire-drawnunder moderate condition during the sintering operation or before thecomposite loses heat. The wire-drawing is preferably performed duringthe sintering stage.

In still another variation, the outer metal pipe may have a plurality ofaxial recesses or holes or bores in which the material powder is filledwhich is sintered according to the process described hereabove. In thisstructure, the outer metal pipe functions as a heat radiant passageduring quenching stage and a bypass of electric current whensuperconductivity is broken.

It is apparent from the description abovementioned that there is nopossibility of chemical reduction of the sintered compound oxide withthe outer metal pipe and hence the superconductor is stabilizedchemically, because the pipe is made of precious metal or has aninterface layer made of precious metal. Namely, the resulting ceramicwire exhibits improved property of superconductivity due to its crustalstructure and oxygen deficiency which are critical factor in perovskitetype or quasi-perovskite type superconductors is assured. Still more,sine the composite of the present invention is isolated from oxidatativeatmosphere because of the presence of the outer metal sheath, theperovskite type or quasi-perovskite type superconductors which has nothigher resistance to oxidation can be protected from surroundingatmosphere effectively.

The composites obtained by the present invention can be utilized assuperconducting wires or parts due to their high and stable Tc.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Superconductor

One of preferred embodiment of the compound oxide from which thesuperconductor is composed is a compound oxide represented by thegeneral formula:

    (α1.xβx)γyOz

in which α stands for an element selected from IIa group of the PeriodicTable, β stands for an element selected from IIIa group of the PeriodicTable and γ stands for an element selected from a group comprising Ib,IIb, IIIb and VIII group of the Periodic Table, and a small letter of"x" represents an atomic ratio of β and is a number which satisfies arange of 0.1≦x≦0.9 with respect to the total of (α+β) which is equal to1, small letters of "y" and "z" represent atomic ratios of γ and oxygen(O) respectively and satisfy ranges of 1.0≦y≦4.0 and 1≦z≦5 respectively.

The superconducting compound oxide have preferably perovskite typestructure or quasi-perovskite type structure. The term of"quasi-perovskite type structure" means any oxide that can be consideredto have such a crystal structure that is similar to perovskite-typeoxides and may include an orthohombically distorted perovskite or adistorted oxygen-deficient perovskite or the like.

In practice, the element α is preferably selected from Ba, Sr and/or Caand the element β is preferably selected from Y, La and/or lanthanidsuch as Sc, Ce, Gd, Ho, Er, Tm, Yb, Lu and the element γ is preferablyCu. It can be mentioned, as preferred compound oxides obtained bycombinations of these elements, Ba-Y-Cu-O type oxide such as YBa₂ Cu₃O₇₋δ, Ba-La-Cu-O type oxide or Sr-La-Cu-O type oxide such as [La_(1-x),Ba_(x) ]₂ CuO_(4-y), in which x and y are numbers which are less than 1.In case of Ba-Y-Cu type compound oxides, a proportion of from 10 to 80%of Ba may be substituted by one or two elements selected from a groupcomprising Mg, Ca and Sr and/or a proportion of from 10 to 80% of Y maybe substituted by one or two elements selected from a group comprisingLa and lanthanid. If the proportions of the substituents become outsideof the abovementioned range of from 10 to 80%, no improvement ofsuperconductivity is expected.

In the preferred embodiment, the compound oxide type superconductor canbe prepared from a material powder which may be (i) a powder mixture ofoxide powders or carbonate powders of constituent elements of a compoundoxide to be produced, such as BaCO₃, Y₂ O₃, CuO or (ii) a sinteredpowder of compound oxide prepared by sintering the powder mixture of (i)and then by pulverizing obtained sintered mass such as YBa₂ Cu₃ O_(7-d)or [La_(1-x), Ba_(x) ]₂ CuO_(4-y).

The sintered powder mixture (ii) is preferable to facilitate control ofproportions of the constituent elements in the material powder in orderto obtain a uniform product of sintered compound oxide having a properproportions of the constituent elements.

The material powder may be prepared also from fluoride, nitrate,sulfate, or the like in addition to or in place of the oxide andcarbonate.

According to a preferred embodiment, additional operations such aswire-drawing, heat-treatment or annealing can be carried out before orafter or during the sintering operation. Namely, after a powder mixtureof compounds is compacted in a metal pipe made of precious metals suchas gold, silver or platinum metals, the pipe is subjected to a series ofoperations comprising annealing, wire-drawing and sintering.

The wire-drawing may be performed by any means including dies, rollerdies, rolling mill, swaging units or extruder. The sintering can becarried out at a temperature ranging between an upper limit which isdefined by a melting point which corresponds to the lowest melting pointof any one of constituent components in the material powder and a lowerlimit which is lower by 100° C. than said upper limit. The annealing canbe carried out at a temperature which is lower than the sinteringtemperature, preferably lower than 160° C. Cooling of heated compositeafter the annealing and sintering operations is carried out at a coolingspeed of lower than 50° C./min, more particularly lower than 10° C./min.It is also possible to remove the outer metal pipe after the annealingor wire-drawing.

According to another preferred embodiment, after a powder mixture ofcompounds is compacted in a metal pipe made of silver, the pipe issubjected to a series of operations comprising annealing, wire-drawing,intermediate sintering, wire-drawing and sintering.

According to still another preferred embodiment, an additional outermetal layer is formed on an outer surface of the pipe. Namely, after apowder mixture of compounds is compacted in a metal pipe and the pipe issubjected to annealing and wire-drawing, an additional outer metal layeris applied on the outer surface of the pipe and then the resulting pipeis wire-drawn before the composite is heated to sinter the materialpowder.

In this case, the additional outer metal layer can be formed by platingtechnique or caulking or cladding technique in which a metal pipe havinga larger inner diameter than the composite pipe is put on the compositepipe and then is caulked tightly on the outer surface of the compositepipe. In this case also, after the pipe filled with the material powdertherein is wire-drawn, it is possible to remove the outer metal pipe atthe same time when the material powder is sintered. The sinteredcomposite is cooled at a lower cooling speed.

The dimensional reduction ratio of the wire-drawing is preferably withina rage of 16 to 92%.

According to still another embodiment, after a powder mixture ofcompounds is compacted in a metal pipe and the pipe is wire-drawn, thepipe is subjected to a series of operations comprising annealing,wire-drawing and sintering. The steps from the wire-drawing, annealingand second wire-drawing may be repeated for several times.

Another type superconductors which are applicable to the presentinvention include following compound oxides:

(i) a compound oxide including at least two elements α1 and α2 selectedfrom IIa group of the Periodic Table, an element δ selected from Vagroup of the Periodic Table and an element γ selected from a groupcomprising Ib, IIb, IIIb and VIII group of the Periodic Table.Particularly, the elements α1 and α2 are preferably Sr and Ca, theelement δ is preferably Bi and the element γ is preferably Cu such as acase of Ca-Sr-Bi-Cu type oxides for example Ca₂ Sr₄ Bi₄ Cu₆ O₂₀₋δ, and(ii) a compound oxide including at least two elements α1 and α2 selectedfrom IIa group of the Periodic Table, an element ε selected from IIIagroup of the Periodic Table and an element γ selected from a groupcomprising Ib, IIb, IIIb and VIII group of the Periodic Table.Particularly, the element α1 and α2 is preferably Ba and Ca, the elementδ is preferably Tl and the element γ is preferably Cu such as a case ofTl₄ Ba₄ Ca₄ Cu₆ O₂₀₊δ.

Now, the process according to the present invention will be describedwith reference to illustrative Examples, but the scope of the presentinvention should not be limited thereto.

EXAMPLE 1

A powder mixture of Ba(NO₃)₂, Y(NO₃)₃ and CuO each having purity of99.9% was kneaded at a atom ratio of Y:Ba:Cu=1:2:3 in ethanol and thensintered previously at 700° C. for 3 hours. The sintered mass obtainedwas then pulverized in a ball mill to prepare a sintered powder having aparticle size of less than 10 μm.

The sintered powder was compacted in a pipe made of silver having anouter diameter of 10 mm and a wall thickness of 1 mm and then sinteredat 910° C. for 7 hours. At the end of the sintering stage and during thepipe is in a heated condition, the pipe was subjected to wire-drawing toreduce its outer diameter to 8 mm and then cooled at a cooling speed of15° C./min.

Then, the pipe was re-heated at 300° C. for 20 minutes and then cooledat a cooling speed of 10° C./min.

According to a usual method, two pairs of electrodes were soldered on asample (30 cm long) cut from the resulting composite with silver pasteand then the sample was immersed in liquidized nitrogen in a cryostat tocool the composite down to a temperature where no resistance wasobserved. Then, the temperature dependence of resistance of the samplewas determined with rising the temperature gradually. The resultsrevealed that the sample of wire showed a temperature of 117 K. where anordinary resistance was observed.

The temperature dependence of resistance was determined by four probemethod in cryostat and temperature was measured by a calibratedAu(Fe)-Ag thermocouple.

The superconducting property of this sample was preserved up to acurvature of 100 mm under a curved congiguration.

EXAMPLE 2

The same procedure as Example 1 was repeated except that the sinteredpowder was compacted in a pipe made of platinum.

The result revealed that the sample obtained showed the same temperatureof 117 K. where an ordinary resitance was observed as Example 1.

EXAMPLE 3

20.8% by weight of commercially available Y₂ O₃ powder, 54.7% by weightof commercially available BaCO₃ and 24.5% by weight of commerciallyavailable CuO were mixed in an attoriter in wet and then dried. Thedried powder was press-molded at a pressure of 100 kg/cm² and thensintered at 880° C. in air for 24 hours and then was pulverized andpassed through a sieve to obtain powder of 100 mesh-under. Theabovementioned operations from the sintering to screening were repeatedfor three times.

After treatment of granulation, the granulated material powder wascompacted into a platinum pipe having an outer diameter of 5 mm, aninner diameter of 4 mm and a length of 1 m and opposite ends of the pipewere closed.

The resulting platinum pipes filled with the material powder wassubjected to wire-drawing to reduce its outer diameter down to 4 mm andthen was heated in air to sinter the material powder at 930° C. for 3hours during which the outer platinum pipe was peeled off by a diethrough which the pipe was passed. After then, the product was cooled ata cooling speed of 8° C./min to obtain a sintered ceramic wire having athin film layer of platinum 0.05 mm thick.

Observation of a cross section of the sintered ceramic wire revealedsuch a fact that a thin surface layer of 0.4 mm thick of the ceramicwire turn red because CuO was reduced to Cu while the central portion ofthe sintered ceramic wire was left in a dark green color of perovskite.Measurement of the critical temperature (Tc) of this superconductingwire of perovskite showed a value of 45 K.

The same procedure was repeated as above except that a finer platinumpipe having an outer diameter of 3 mm and an inner diameter of 2 mm wasused and wire-drawn with higher dimensional reduction ratio of up to afinal outer diameter of 2.4 mm. In this case, no reduction of CuO wasobserved but the resulting sintered ceramic wire consisted totally ofthe perovskite having the critical temperature of 97 K.

EXAMPLE 4

20.8% by weight of commercially available Y₂ O₃ powder, 54.7% by weightof commercially available BaCO₃ and 24.5% by weight of commerciallyavailable CuO were mixed in an attoriter in wet and then dried. Thedried powder was press-molded at a pressure of 100 kg/cm² and thensintered at 880° C. in air for 24 hours and then was pulverized andpassed through a sieve to obtain powder of 100 mesh-under. Theabovementioned operations from the sintering to screening were repeatedfor three times.

The obtained sintered material powder was compacted into a platinum pipehaving an outer diameter of 5 mm, an inner diameter of 4 mm and a lengthof 1 m and opposite ends of the pipe were closed. The resulting platinumpipe filled with the material powder was heated to 600 ° C. and thenannealed.

20 samples of the annealed platinum pipes were passed through a seriesof roller dies to obtain the final outer diameter of 1.0 mm under suchcondition that the dimensional reduction ratio in cross sectionaldirection per one reduction unit block was 38%. In this case, breakageof pipes were observed at such frequencies as are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Diameter when breakage occurred                                                                    Frequency of breakage                                    ______________________________________                                        No breakage occurred up to 1.0 mm                                                                  1                                                        Breakage occurred between                                                                          8                                                        1.0 mm and 1.1 mm                                                             Breakage occurred between                                                                          7                                                        1.1 mm and 1.5 mm                                                             Breakage occurred between                                                                          3                                                        1.5 mm and 2.0 mm                                                             Breakage occurred between                                                                          1                                                        2.0 mm and 2.4 mm                                                             ______________________________________                                    

The same procedure as above was repeated except that the Pt pipes filledwith the sintered powder were wire-drawn through a stationary die. Inthis case, the frequency of breakage increased five times more than theabovementioned wire-drawing by roller dies.

Both of five samples prepared by roller dies and one sample which couldbe drown up to a diameter of 1.0 mm without any breakage by theconventional stationary die were sintered at 750° C. for 20 minutes.Then, reduction in cross section of the pipes was repeated by the rollerdies and by the stationary dies for respective samples to obtain anouter diameter of 0.3 mm. The result revealed that the five samplespassed through roller dies could be drawn up to the final diameter of0.3 mm, while the one sample passed through the stationary die broke ata diameter of 0.42 mm.

Then, all of the samples were subjected to the final sintering at 850°C. for 5 hours. When the sintering completed, the composite was cooledat a cooling rate of 10° C./min. Then, the critical temperature (Tc) wasmeasured on the sample which was passed through roller dies to adiameter of 0.3 mm and sintered at 930° C. for 3 hours.

Measurement of the critical temperature was carried out by aconventional four probe method in which, after electrodes were connectedto the resulting wire with conductive silver paste, the wire wasimmersed in liquidized hydrogen to cool the wire down to a temperatureof 25 K. in a cryostat. Temperature is measured by a calibratedAu(Fe)-Ag thermocouple. Then, the temperature dependence of resistanceof the sample was determined with rising the temperature gradually. Theresults revealed that the sample of the present invention exhibitedsuperconductivity up to relatively higher temperature of 99 K.

For comparison, the critical temperature of the sample prepared by thestationary die was also measured The result revealed that the criticaltemperature of the comparative example is 20 K. lower than the criticaltemperature of the sample prepared by the roller dies. This discrepancymight be caused by fine cracks produced inside the ceramic wire. Thisfact was also supported by measurement of current density in which thesample obtained by the roller dies showed higher critical density thanthe sample prepared by the stationary dies.

EXAMPLE 5

The same sintered material powder as Example 4 was used and wascompacted into a platinum pipe having an outer diameter of 5 mm, aninner diameter of 4 mm and a length of 1 m and opposite ends of the pipewere closed. The resulting platinum pipe filled with the material powderwas heated to 880° C. for 2 hours and then annealed. The annealedplatinum pipes was passed through a series of roller dies to reduce toan outer diameter of 4.1 mm.

Then, after the pipe was further heated at 900° C. for 1 hours and thenannealed, its diameter was further reduced to 3.2 mm. A piece of theresulting pipe was slitted axially and examined microscopically to findinnumerable cracks of less 0.8 mm width in the sintered ceramic masswhich might be caused by cold working on the sintered ceramic.

The ceramic wire of 3.2 mm in diameter was then further heated at 930°C. for 5 hours and cooled slowly at a cooling speed of 10° C./min. Theresulting pipe was slitted again axially and examined microscopically tofind no crack. The critical temperature of this ceramic wire was 101 K.The critical temperature and resistance were determined by the samemethod as Example 4.

EXAMPLE 6

The same procedure as Example 4 was repeated to obtain samples ofcomposites each having an outer diameter of 0.3 mm and comprising anouter platinum pipe and a sintered mass surrounded tightly by theplatinum pipe. The samples were however lacking in uniformity, namelythe variation in diameter of these samples was ±0.16 mm. Still more, theouter platinum pipe had not enough strength to breakage.

Therefore, another platinum pipe having an outer diameter of 3 mm and aninner diameter of 1.5 mm was put on one of the samples having an outerdiameter of 1.0 mm obtained in Example 4 and was caulked to obtain acladded composite. This cladded composite was further wire-drawn to adiameter of 1.5 mm and then sintered at 930° C. for 3 hours and cooledslowly at a cooling speed of 10° C./min. The resulting product showed auniform appearance and had the reduced variation in diameter of ±0.005mm. This product maintained a relatively higher superconductivity up to97 K. The critical temperature and resistance were determined by thesame method as Example 4.

EXAMPLE 7

85.5% by weight of commercially available La₂ O₃ powder, 3.1% by weightof commercially available SrCO₃ and 11.4% by weight of commerciallyavailable CuO were mixed in an attoriter in wet and then dried. Thedried powder was press-molded at a pressure of 100 kg/cm² and thensintered at 900° C. in air for 20 hours and then was pulverized andpassed through a sieve to obtain powder of 100 mesh-under.

After the obtained sintered material powder was granulated, it wascompacted into a platinum pipe having an outer diameter of 5 mm, aninner diameter of 4 mm and a length of 1 m and opposite ends of the pipewere closed. The resulting platinum pipe filled with the material powderwas heated to 1,050° C. for 2 hours, resulting in that almost all ofplatinum was fused off the sintered ceramic core to obtain a wire of 7.7mm long coated with a Pt layer of 0.01 to 0.06 mm thick. The variationin diameter reduced to ±0.006 mm. This product maintained a relativelyhigher superconductivity up to 105 K. The critical temperature andresistance were determined by the same method as Example 4.

EXAMPLE 8

Powders of Ba, Y₂ O₃ and CuO were used. A mixture of 20.8% by weight ofY₂ O₃ powder, 54.7% by weight of Ba powder and 24.5% by weight of CuOpowder were mixed in a molter and was press-molded. The resultingcompact was sintered at 940° C. for 15 hours. The sintered mass was thenpulverized and passed through a sieve to obtain powder of 100mesh-under. The sequence of the press-molding, sintering andpulverization was repeated for three times to obtain a material powder.

Following four kinds of pipes were used:

(i) Copper pipe having an outer diameter of 20 mm and an inner diameterof 1.5 mm,

(ii) Silver pipe having an outer diameter of 20 mm and an inner diameterof 15 mm,

(iii) Copper pipe having an outer diameter 20 mm and an inner diameterof 15 mm and having a inner lining layer of silver, and

(iv) Copper pipe having an outer diameter of 20 mm and an inner diameterof 15 mm and having a inner lining layer of gold,

After the sintered material powder was compacted in these pipes,opposite ends of each pipe were closed. Then, the pipes were subjectedto swaging work to reduce their outer diameter to 6 mm. The resultingpipes filled with the material powder were heated to 950° C.

The critical temperatures of the resulting composites were determined bythe same method as Example 4. The result is shown in the followingTable:

    ______________________________________                                        pipe      Critical temperature (K.)                                           ______________________________________                                        (i)       63                                                                  (ii)      94                                                                  (iii)     92                                                                  (iv)      93                                                                  ______________________________________                                    

EXAMPLE 9

The same sintered material powder as Example 4 was used and wascompacted into a variety of silver-copper alloy pipes each having anouter diameter of 5 mm, an inner diameter shown in the following Tableand a length of 1 m. Then, the pipes were subjected to wire-drawing workto reduce their diameters to 3.6 mm.

These pipes filled with the material powder were heated to 930° C. for 3hours in air to obtain sintered ceramic wires covered with Ag-Cu alloycoating.

Each samples of the resulting pipes were cut to be examinedmicroscopically to find no chemical reduction of sintered oxide to CuObut to find formation of a layer of Ag-CuO cuased by internal oxidationof the Ag-Cu pipes.

The following Table summerrizes the kind of alloys used, the innerdiameters of the pipes, and the critical temperatures of the resultingcomposites.

    ______________________________________                                                                            Critical                                                   Vickers   Inner    temperature                               No   alloy       Hardness  Dia. (mm)                                                                              (K.)                                      ______________________________________                                        1    Ag--2.8%Cu  42        4        63                                        2    Ag--2.8%Cu  42        4.3                                                3    Ag--10%Cu   64        4        66                                        4    Ag--10%Cu   64        4.3      70                                        5    Ag--20%Cu   85        4        62                                        6    Ag--20%Cu   85        4.3      69                                        7    Ag--30%Cu   103       4        65                                        8    Ag--30%Cu   103       4.5      78                                        ______________________________________                                    

EXAMPLE 10

The same powder mixture as Example 1 was compacted in a Ag-30% Cu alloypipe and having an outer diameter of 5 mm and a wall thickness of 1 mmand then sintered at 910° C. for 7 hours. At the end of the sinteringstage and during the pipe is in a heated condition, the pipe wassubjected to wire-drawing to reduce its outer diameter to 3.5 mm andthen cooled at a cooling speed of 15° C./min.

Then, the pipe was re-heated at 300° C. for 20 minutes and then cooledat a cooling speed of 10° C./min.

According to a usual method, two pairs of electrodes were soldered on asample (30 cm long) cut from the resulting composite with indium pasteand then the temperature dependence of resistance of the sample wasdetermined with rising the temperature gradually. The results revealedthat the sample of wire showed a temperature of 74 K. where an ordinaryresistance was observed.

The temperature dependence of resistance was determined by the samemethod as Example 1.

The superconducting property of this sample was preserved up to acurvature of 100 mm under a curved congiguration.

EXAMPLE 11

The same material powder as Example 3 was compacted in a Ag-20% Cu alloypipe having an outer diameter of 5 mm and an inner diameter of 4 mm andopposite ends of the pipe was closed.

The pipe filled with the material powder therein was subjected towire-drawing work to reduce its outer diameter to 4 mm and then washeated at 930° C. for 3 hours to sinter the material powder. Theresuclting composite was cooled slowly at a cooling speed of 8° C./minto obtain a sintered ceramic wire coated with a Ag-20% CuO alloy layerof 0.05 mm thick.

No chemical reduction of the sintered ceramic wire was observed on across section thereof but appearance of perovskite color was observed.

The critical temperature of this superconducting wire was 75 K.

EXAMPLE 12

The same dried powder as Example 7 was press-molded at a pressure of 100kg/cm² and then sintered at 840° C. in air for 3 hours and then waspulverized and passed through a sieve to obtain powder of 100mesh-under.

After the obtained sintered material powder was granulated, the materialpowder was compacted in a Ag-10% CU alloy pipe having an outer diameterof 5 mm, an inner diameter of 4 mm and a length of 1 m and opposite endsof the pipe was closed.

The pipe filled with the material powder therein was subjected towire-drawing work to reduce its outer diameter to 3.4 mm and then washeated at 940° C. for 12 hours in vaccum to sinter the material powder.The resulting wire coated with a Ag-10% CuO alloy layer of 0.01 to 0.06mm thick.

The critical temperature of this superconducting wire was 79 K.

What is claimed is:
 1. A composite comprising an outer metal pipe and asuperconducting portion including a high Tc superconductor of compoundoxide, said outer metal pipe surrounding said superconducting portion,characterized in that said outer metal pipe is made of at least one ofmetals selected from a group consisting of Ag, Au, Pd, Pt, Rh, Ir, Ru,Os and their alloys.
 2. A composite set forth in claim 1, charcterizedin that said compound oxide superconductor is in a form of a sinteredsolid mass compacted in said outer metal pipe.
 3. A composite set forthin claim 1, characterized in that a plurality of metal wires areembedded in said compound oxide superconductor.
 4. A compositecomprising a high Tc superconductor of compound oxide and an outer metalpipe which surrounds said superconductor, characterized in that saidouter metal pipe is made of at least one of metals selected from a groupconsisting of Ag, Au, Pd, Pt, Rh, Ir, Ru, Os and their alloys furthercharacterized in that said outer metal pipe is perforated so that a partof the compound oxide superconductor supported by the outer metal pipeis opened to surrounding atmosphere.
 5. A composite set forth in claim4, characterized in that said outer metal pipe is a cylindrical wirenetting.
 6. A composite set forth in claim 1, characterized in that saidinner surface of said outer metal pipe has a layer resisting againstoxidation which is inactive to the compound oxide.
 7. A composite setforth in claim 6, characterized in that said oxidation resisting layeris composed of an oxide of a material of which said outer metal layer ismade.
 8. A composite set forth in claim 1, characterized in that saidcompound oxide superconductor is in a form of a layer deposited on theinner surface of an outer metal pipe to provide an axial hollow interiorpassage being formed in the metal pipe.
 9. A composite set forth inclaim 8, characterized in that said outer metal pipe is closed atopposite ends thereof.
 10. A composite set forth in claim 8,characterized in that the axial hollow interior passage in said outermetal pipe is filled with an inert gas.
 11. A composite set forth inclaim 8, characterized in that a coolant is circulated through aninterior of said axial hollow interior passage.
 12. A composite setforth in claim 1, characterized in that said compound oxide is acompound oxide including an element α selected from IIa group of thePeriodic Table, an element β selected from IIIa group of the PeriodicTable and an element γ selected from a group comprising Ia, IIb, IIIband VIII group of the Periodic Table.
 13. A composite set forth in claim12, characterized in that said compound oxide is of quasi-perovskitetype oxide.
 14. A composite set forth in claim 12, characterized in thatsaid element α is Ba, said element β is Y and said element γ is Cu. 15.A composite set forth in claim 12, characterized in that said element αis Ba, said element β is La and said element γ is Cu.
 16. A compositeset forth in claim 12, characterized in that said element α is Sr, saidelement β is La and said element γ is Cu.
 17. A composite set forth inclaim 1, characterized in that said compound oxide is a compound oxideincluding at least two elements α1 and α2 selected from IIa group of thePeriodic Table, an element δ selected from Va group of the PeriodicTable and an element γ selected from a group comprising Ia, IIb, IIIband VIII group of the Periodic Table.
 18. A composite set forth in claim17, characterized in that said element α1 and α2 is Sr and Ca, saidelement δ is Bi and said element γ is Cu.
 19. A composite set forth inclaim 1, characterized in that said compound oxide is a compound oxideincluding at least two elements α1 and α2 selected from IIa group of thePeriodic Table, an element ε selected from IIIa group of the PeriodicTable and an element γ selected from a group comprising Ia, IIb, IIIband VIII group of the Periodic Table.
 20. A composite set forth in claim19, characterized in that said element α1 and α2 is Ba and Ca, saidelement δ is Tl and said element γ is Cu.
 21. A composite comprising ahigh Tc superconductor of compound oxide and an outer metal pipe whichsurrounds said superconductor, characterized in that said outer metalpipe is made of at least one of metals selected from a group consistingof Ag, Au, Pd, Pt, Rh, Ir, Ru, Os and their alloys wherein said compoundoxide is represented by the general formula:

    (α1-xβx)γyOz

in which α stands for an element selected from IIa group of the PeriodicTable, β stands for an element selected from IIIa group of the PeriodicTable and γ stands for an element selected from a group comprising Ia,IIb, IIIb and VIII group of the Periodic Table, and a small letter of"x" represents an atomic ratio of β and is a number which satisfies arange of 0.1≦x≦0.9 with respect to the total of (α+β) which is equal to1, small letters of "y" and "z" represent atomic ratios of γ and oxygen(O) respectively and satisfy ranges of 1.0≦y≦4.0 and 1≦z≦5 respectively.22. A composite set forth in claim 1, characterized in that said outermetal pipe directly contacts said superconductor.
 23. A composite setforth in claim 2, characterized in that said sintered solid mass forms acore within said outer metal pipe and said core consists of saidcompound oxide.
 24. A composite set forth in claim 1, characterized inthat said superconducting portion consists of said compound oxide.
 25. Acomposite set forth in claim 1, characterized in that said compoundoxide is selected from the group consisting of YBCO and La-Sr-Cu-O andsaid outer metal pipe is made of at least one metal selected from agroup consisting of Ag, Pt, Cu, and their alloys.